MSVC compiler now assumes UTF-8 source code by default

Every project that uses UTF-8 source files had to add manually /utf-8 C/C++ compiler argument for MSVC otherwise they wouldn't work on non-English locale. Meson now switched the default to UTF-8 to be more consistent with all other compilers.

This can be overridden but using /source-charset:

if cc.get_id() == 'msvc'
  add_project_arguments('/source-charset:.XYZ', language: ['c', 'cpp'])
endif

See Microsoft documentation for details: https://docs.microsoft.com/en-us/cpp/build/reference/source-charset-set-source-character-set.